@lume/element
Advanced tools
Create Custom Elements with reactivity and automatic re-rendering.
Easily and concisely write Custom Elements with simple templates and reactivity.
Use the custom elements on their own in plain HTML or vanilla JavaScript, or in Vue, Svelte, Solid.js, Stencil.js, React, and Preact, with full type checking, autocompletion, and intellisense in all the template systems of those frameworks, in any IDE that supports TypeScript such as VS Code.
Write your elements once, then use them in any app, with a complete developer experience no matter which base component system your app uses.
npm install @lume/element:bulb:Tip:
If you are new to Custom Elements, first learn about the basics of Custom Element APIs available natively in browsers. Lume Element simplifies the creation of Custom Elements compared to writing them with vanilla APIs, but sometimes vanilla APIs are all that is needed.
Define a <click-counter> element:
import {Element, element, numberAttribute} from '@lume/element'
import html from 'solid-js/html'
import {createEffect} from 'solid-js'
@element
class ClickCounter extends Element {
@numberAttribute count = 0
template = () => html`<button onclick=${() => this.count++}>Click! (count is: ${() => this.count})</button>`
css = `
button {
border: 2px solid deeppink;
margin: 5px;
}
`
connectedCallback() {
super.connectedCallback()
// Log the `count` any time it changes:
createEffect(() => {
console.log('count is:', this.count)
})
}
}
Use the <click-counter> in a plain HTML file:
<body>
<click-counter></click-counter>
<!-- Manually set the `count` value in HTML: -->
<click-counter count="100"></click-counter>
<script type="module">
import './click-counter.js'
// Manually set the `count` value in JS:
document.querySelector('click-counter').count = 200
</script>
</body>
Example on CodePen (without decorators)
[!Note] Once decorators land in browsers, the above example will work out of the box as-is without compiling, but for now a compile step is needed for using decorators.
JSX can be used for the
templateof an element, but that will always require compiling:template = () => <button> Click! (count is: {this.count}) </button>Further examples below show how to define elements without decorators or JSX, which works today without a compiler.
Use the <click-counter> in another element's template,
import {Element, element} from '@lume/element'
import html from 'solid-js/html'
import {signal} from 'classy-solid'
@element('counter-example')
class CounterExample extends Element {
@signal count = 50 // Not an attribute, only a signal.
template = () => html`<click-counter count=${() => this.count}></click-counter>`
}
document.body.append(new CounterExample())
Use <click-counter> in a plain function component (i.e. a Solid.js component):
// At this point this, this boils down to plain Solid.js code (`@lume/element` comes
// with `solid-js`)
import {createSignal} from 'solid-js'
import html from 'solid-js/html'
function CounterExample() {
const [count, setCount] = createSignal(50)
return html`<click-counter count=${count()}></click-counter>`
}
document.body.append(CounterExample())
Custom
Elements
(also known as Web
Components are a
feature of browsers that allow us to define new HTML elements that the browser
understands in the same way as built-in elements like <div> or <button>.
They are very useful for organizaing web apps into separately and sometimes
re-usable pieces (elements).
If that flew over your head then you might first want to try a beginner HTML tutorial. You will also need to some basic knowledge of JavaScript.
@lume/element provides a set of features that make it easier to manipulate
elements and to define new custom elements and easily compose them together
into an application.
With @lume/element we can create custom elements that have the following
features:
html template tag, that automatically update when reactive instance properties are used in the templates.@attribute decorators on class fields.
@attribute receive values from HTML attributes
(with the same name but dash-cased) when the HTML attribute values change.classy-solid: utilities for using
Solid.js patterns on classes, such as the @signal
decorator for making class fields reactive (backed by Solid signals).
Decorators from @lume/element compose the @signal decorator to make
properties be reactive.html template string tag,
which does not require a build step.@lume/element applies
its own style scoping for the element at the nearest root node.STUB: This section needs expansion, but should be enough for anyone familiar with common build tooling in the webdev/JS ecosystem. Contributions very welcome!
Follow the guide on installing lume from
CDN, but simply replace
lume with @lume/element. The process is otherwise the same.
The examples here in the README follow the CDN approach to keep things simple, for example.
[!Note] Decorator syntax and JSX syntax are both not supported with this install method as it does not use a build step. In the near future, decorators will be out natively in browsers and JS engines (but not JSX).
This assumes some familiarity with command lines and JavScript build tools.
First make sure Node.js is installed so that we have the npm package manager avaiable.
Install the @lume/element package using the following in a terminal:
npm install @lume/element
In order to use decorators today (recommended), we need to compile
them with TypeScript 5 or higher (recommended, even if writing JS and not TS, as
decorator syntax works out of the box with TypeScript), or use the Babel
compiler with
@babel/plugin-proposal-decorators.
npm install --save-dev typescript
# or
npm install --save-dev @babel/cli @babel/core @babel/plugin-proposal-decorators
If using TypeScript, set allowJs in tsconfig.json to allow compiling JS files, f.e.:
{
"compilerOptions": {
"allowJs": true,
"outDir": "dist"
},
"include": ["./src/**/*"]
}
and running npx tsc. See the TypeScript section below for configuring JSX
types for various frameworks (Solid, React, Preact, etc).
If using Babel, add the decorators plugin to .babelrc, f.e.
{
"plugins": ["@babel/plugin-proposal-decorators"]
}
and running npx babel src --out-dir dist.
If you'd like to use the HTML-like markup inside JavaScript known as "JSX",
instead of Solid's html template
tag which
requires no build, the
babel-preset-solid package will also
be needed:
npm install --save-dev babel-preset-solid
Configure Babel to use the preset inside your project's .babelrc file or in
your Webpack babel-loader config:
{
"plugins": ["@babel/plugin-proposal-decorators"],
"presets": ["solid"]
}
[!Note] If compiling decorators with TypeScript, Babel is still needed for Solid JSX because TypeScript does not compile JSX into Solid.js format, only into React format. Either compile decorators with TypeScript and have Babel compile JSX in a second step, or compile both decorators and JSX with Babel in a single step.
A great way to create re-usable components is to create Custom Elements. The advantage of custom elements is that they follow web standards, and therefore they can be used in any web application and manipulated by any DOM manipulation libraries like jQuery, React, Vue, Svelte, or Angular, Solid.js, and all the rest.
The following is a custom element definition with a reactive property
firstName that also accepts values from an attribute named first-name (the
property name is converted to dash-case for the attribute name).
[!Note] Deorators and JSX are not required. The non-decorator and non-JSX forms are shown further below. The Decorators section has details on each decorator available.
import {
Element, // A base class for LUME custom elements
element, // A decorator for defining elements, required for reactive JS properties.
attribute, // A property decorator to map attributes to properties, and that makes properties reactive
eventAttribute, // A property decorator that causes values from the attributes/properties to be set as an event listener for the respective event, just like built-in "onclick" attributes/properties.
css, // A no-op identity template tag function (useful to enable CSS syntax highlighting in various text editors)
// Decorators for defining specific attributes types (string values are coerced to the respective JS type):
stringAttribute,
numberAttribute,
booleanAttribute,
} from '@lume/element'
@element('greeting-card') // defines the element tag name
class GreetingCard extends Element {
// The firstName property will be a reactive variable, and any value from an
// attribute named 'first-name' will be mapped back to this property (the
// attribute name is the dash-case version of the property name).
@attribute firstName = 'Roger'
// Specific attribute types (the JS property will always be of the specified
// type):
@stringAttribute someString = ''
@numberAttribute someNumber = 123
@booleanAttribute someBoolean = false
// Define event properties to specify which events the element dispatches.
// Besides being useful for type definitions in JSX, these properties work
// like the builtin event properties such as "onclick" (JS property or DOM
// attribute code string).
//
// For example, a user can write `el.onhello = event => {...}` just like
// they can do with builtin event properties like `el.onclick = event =>
// {...}`.
@eventAttribute onhello = null
// Define a DOM tree that we want rendered on screen by providing a
// `template`. The `template` should be a function that returns a DOM
// element or array of DOM elements (which we can create with JSX, or with
// an `html` template tag, or with plain JS). The DOM content will be, by
// default, appended into the ShadowRoot of our custom element.
//
// To take advantage of reactivity in our template, simply interpolate
// properties that were decoratored with an attribute decorator or defined
// with `static observedAttributeHandlers` into the template.
//
// Here, any time the `.firstName` property's value changes, the DOM will be
// automatically updated.
template = () => (
<div>
<span>
Hello <i>{this.firstName}</i>
</span>
{/* Children of a <greeting-card> element get rendered here. */}
<slot></slot>
</div>
)
// Apply styling to this element and its content with the static `css` property.
// Because the property is static, this style is re-used across all instances of the element.
// Styles are by default scoped to the element's content due to ShadowRoot style encapsulation.
static css = css`
:host {
background: skyblue;
}
div {
color: pink;
}
`
// For instance-specific styling, use the non-static `css` property. This
// style has higher precedence over styles in the `static css` property. In
// this example, the divs in each instance of this element will have borders
// of random sizes. Note, `css` is currently not reactive, it runs once
// initially, so using a reactive property in the css will currently not
// update the style.
css = css`
div {
border: ${Math.random() * 5}px solid teal;
}
`
// connectedCallback is a method that fires any time this custom element is
// connected into a web site's live DOM tree.
connectedCallback() {
super.connectedCallback() // Don't forget to call the super method!
// Once the element is connected, let's update the `.firstName` prop after a
// couple of seconds, and we'll see the change on screen.
setTimeout(() => (this.firstName = 'Zaya'), 2000)
// And show that it works by setting HTML attributes too, two seconds later.
setTimeout(() => this.setAttribute('first-name', 'Raquel'), 4000)
// The element may dispatch events.
setTimeout(() => this.dispatchEvent(new Event('hello')), 3000)
}
// Use the disconnectedCallback to clean anything up when the element is removed from the DOM.
disconnectedCallback() {
super.disconnectedCallback()
// ... clean up ...
}
}
Now we can use it in the HTML of a web site, or in the template of another component:
<greeting-card first-name="Raynor" onhello={() => console.log(event.target.firstName, 'says hello')}></greeting-card>
Example on CodePen (without decorators, with Solid's html template tag instead of JSX)
Inside an element's template() method we can assign bits and pieces of DOM to
variables, and we can also use other custom elements and functional components.
Similary, the css property can also be a method:
@element('greeting-card')
class GreetingCard extends Element {
// ... same as before ...
// This time 'template' is a method that has some logic, and refers to pieces of DOM using variables.
template() {
const greeting = (
<span>
Hello <i>{this.firstName}</i>
</span>
)
console.log(greeting instanceof HTMLSpanElement) // true
// One piece of DOM can be composed into another:
const result = <div>{greeting}</div>
console.log(result instanceof HTMLDivElement) // true
return result
}
// ... same as before ...
css() {
const thickness = Math.random() * 5
return css`
div {
border: ${thickness}px solid teal;
}
`
}
// ... same as before ...
}
Lume Element is built on Solid.js, so we can also use Solid.js at the top level
of a module for example. This sort of code can be useful in the template of a
custom element, or the body of a functional component.
import {createSignal} from 'solid-js'
// Make a signal with an initial value of 0.
const [count, setCount] = createSignal(0)
// Increment the value of count every second.
setInterval(() => setCount(count() + 1), 1000)
// Create a <div> element with a child <h1> element. The data-count attribute
// and the text content of the <h1> element will automatically be updated whenever
// the count variable changes.
const el = (
<div>
<h1 data-count={count()}>The count is: {count()}</h1>
</div>
)
// The result stored in the `el` variable is a `<div>` element! For example,
// we can call regular DOM APIs like `setAttribute` on it.
el.setAttribute('foo', 'bar')
// Append the element to the body of the page, and now we'll see a
// continually-updating message on the screen.
document.body.append(el)
Example on CodePen (with Solid's html template tag instead of JSX)
Continuing with the same count variable from the previous example, here's how
to compose DOM trees using "functional components". This is plain Solid.js, and
functional components (Solid.js components) can be used in a custom element's
template.
A functional component is a function that simply returns one or more DOM
elements. JSX expressions and the html template string tag both return the top
level elements defined in the markup.
// This is just plain Solid.js code. See https://solidjs.com for more on writing
// functional components.
// This Label functional component uses the empty <></> tag to contain more than
// one root-level child, and the return value will be an array of DOM nodes.
const Label = props => (
<>
<div>{props.greeting}</div>
{props.children}
</>
)
// This Greeting functional component nests the content of the Label component
// in its template, and the <div> inside the <Label> gets distributed to the
// part of the Label component where we see `{props.children}`.
const Greeting = () => (
<section>
<Label greeting={'hello (' + count() + ')'}>
<div>John</div>
</Label>
</section>
)
// The `Greeting` function only needs to be called once, and it will return a
// reference to an element or multiple elements. The `Greeting` function does
// NOT need to be called over and over to re-render like in some other libraries
// (for example React). That's what makes all of this simple and clean. The
// reactivity inside the component templates takes care of updating content of
// the created DOM tree.
// Here `elem` will be a reference to an actual `<section>` element that the
// `Greeting` function returned.
const elem = Greeting()
// It's just DOM! Use regular DOM APIs to append the element to the body.
document.body.append(elem)
Example on CodePen (with Solid's html template tag instead of JSX)
Continuing from above, here's a custom element that re-uses the Greeting
component. This shows that any regular Solid.js component can be
used in the template of a custom element made with @lume/element:
@element // The 'cool-element' name is implied from the constructor name (dash-cased)
class CoolElement extends Element {
template = () => (
<>
<h2>Here's a greeting:</h2>
<Greeting />
</>
)
}
document.body.insertAdjacentHTML('beforeend', `<cool-element></cool-element>`)
Example on CodePen (without decorators, with Solid's html template tag instead of JSX)
Writing function components can sometimes be simpler, but functional components do not have features that custom elements have such as native style scoping (style scoping with function components requires an additional Solid.js library or compiler plugin), etc.
In contrast to custom elements, functional components only work within the
context of other functional components made with Solid.js or custom elements
made with @lume/element. Functional components are not compatible with HTML,
React, Vue, Angular, Svelte, or all the other web libraries and frameworks. For
portability across applications and frameworks, this is where custom elements
shine.
Custom elements are also debuggable in a browser's element inspector out of the box, while functional components are not (functional components require devtools plugins for each browser, if they even exist). See Lume's Debugging guide for an example.
ElementA base class for custom elements made with @lume/element.
[!Note] The
Elementclass from@lume/elementextends fromHTMLElement.Safari does not support customized built-ins, and neither does
@lume/element, so at the moment we do not support extending from other classes such asHTMLButtonElement, etc.
The Element class provides:
templateA subclass can define a .template that returns a DOM node, and this DOM node
will be appened into the element's ShadowRoot by default, or to the element
itself if .hasShadow is false.
One way to write a template is using Solid
JSX syntax (this will always
require a build step).
import {Element} from '@lume/element'
import {createSignalFunction} from 'classy-solid' // a small wrapper around Solid's createSignal that allows reading and writing from the same function.
class CoolElement extends Element {
count = createSignalFunction(100)
template = () => (
<div>
<span>The count is: {this.count()}!</span>
</div>
)
// ...
}
customElements.define('cool-element', CoolElement)
Another way to write a template is using Solid's html template string tag
(which does not require a build step). Using the following template, the
example can run in a browser without a compile step (note, we're not using
decorators yet):
// ...
template = () => html`
<div>
<span>The count is: ${this.count}!</span>
</div>
`
// ...
Example on CodePen (with html template tag instead of JSX)
[!Note] When
countchanges, the template updates automatically.
We can also manually create DOM any other way, for example here we make and
return a DOM tree using DOM APIs, and using a Solid effect to update the element
when count changes (but we could have used React or jQuery, or anything
else!):
// ...same...
import {createEffect} from 'solid-js'
// ...same...
// Replace the previous `template` with this one:
template = () => {
const div = document.createElement('div')
const span = document.createElement('span')
div.append(span)
createEffect(() => {
// Automatically set the textContent whenever `count` changes (this is a
// conceptually-simplified example of what Solid JSX compiles to).
span.textContent = `The count is: ${this.count()}!`
})
return div
}
// ...same...
static cssUse the static css field to define a CSS string for styling all instances of
the given class. A static property allows @lume/element to optimize by sharing
a single CSSStyleSheet across all instances of the element, which could be
beneficial for performance if there are many thousands of instances.
import {Element} from '@lume/element'
class CoolElement extends Element {
template = () => <span>This is some DOM!</span>
// Style is scoped to our element, this will only style the <span> inside our element.
static css = `
span { color: violet; }
`
}
customElements.define('cool-element', CoolElement)
Example on CodePen (with html template tag instead of JSX)
The static css property can also be a function:
// ...
class CoolElement extends Element {
// ...
static css = () => {
const color = 'limegreen'
return `
span { color: ${color}; }
`
}
// ...
}
Example on CodePen (with html template tag instead of JSX)
:bulb:Tip:
Use the
cssidentity template tag to enable syntax highlighting and code formatting in some IDEs:
import {css} from '@lume/element'
// ...
class CoolElement extends Element {
// ...
static css = css`
span {
color: cornflowerblue;
}
`
// ...
}
cssUse the non-static css property to define styles that are applied per
instance of the given element. This is useful for style that should differ
across instances. This will not be as optimized as static css will be because
it will create one stylesheet per element instance, but the performance
difference will not matter for most use cases.
import {Element, css} from '@lume/element'
class CoolElement extends Element {
template = () => <span>This is some DOM!</span>
// A random color per instance.
#color = `hsl(calc(${Math.random()} * 360) 50% 50%)`
// Style is scoped to our element, this will only style the <span> inside our element.
css = css`
span {
color: ${this.#color};
}
`
}
Example on CodePen (with html template tag instead of JSX)
connectedCallbackNothing new here, this is simply a part of the browser's native Custom Elements
connectedCallback API.
It is triggered when the element is connected into the document. Use it to
create things.
import {Element} from '@lume/element'
class CoolElement extends Element {
connectedCallback() {
// Don't forget to call the super method from the Element class!
super.connectedCallback()
// ...Create things...
}
// ...
}
disconnectedCallbackNothing new here, this is simply a part of the browser's native Custom Elements
disconnectedCallback API.
It is triggered when the element is disconnected from the document. Use it to
clean things up.
import {Element} from '@lume/element'
class CoolElement extends Element {
disconnectedCallback() {
// Don't forget to call the super method from the Element class!
super.disconnectedCallback()
// ...Clean things up...
}
// ...
}
adoptedCallbackNothing new here, this is simply a part of the browser's native Custom Elements
adoptedCallback API.
It is triggered when the element is adopted into a new document (f.e. in an iframe).
import {Element} from '@lume/element'
class CoolElement extends Element {
adoptedCallback() {
// Don't forget to call the super method from the Element class!
super.adoptedCallback()
// ...Do something when the element was transferred into another window's or iframe's document...
}
// ...
}
attributeChangedCallbackNothing new here, this is simply a part of the browser's native Custom Elements
attributeChangedCallback API.
It is triggered when an observed attribute of the element is added, modified,
or removed.
import {Element} from '@lume/element'
class CoolElement extends Element {
static observedAttributes = ['foo', 'bar']
attributeChangedCallback(attributeName, oldValue, newValue) {
// Don't forget to call the super method from the Element class!
super.attributeChangedCallback(attributeName, oldValue, newValue)
// Attribute name is the name of the attribute change changed.
// If `oldValue` is `null` and `newValue` is a string, it means the attribute was added.
// If `oldValue` and `newValue` are both strings, it means the value changed.
// If `oldValue` is a string and `newValue` is `null`, it means the attribute was removed.
}
// ...
}
[!Warning] The
static observedAttributesproperty is required for observing attributes, and specifies which attributes will triggerattributeChangedCallback.attributeChangedCallbackwill not be triggered for any attributes that are not listed instatic observedAttributes!
static observedAttributesNothing new here, this is simply a part of the browser's native Custom Elements
static observedAttributes API.
It defines which attributes will be observed. From the previous example:
class CoolElement extends Element {
static observedAttributes = ['foo', 'bar']
// ...
}
Note! Although static observedAttributes works, it is recommended to use the
static observedAttributeHandlers property instead:
static observedAttributeHandlersThis is an alternative to attribute decorators (recommended, see the Decorators docs below), and will be removed after decorators are supported natively in JS engines.
As an alternative to static observedAttributes, and mainly for non-decorator
users (because not all JS engines support them yet at time of writing this),
observed attributes can be defined with static observedAttributeHandlers, a
map of attribute names to attribute handlers. This requires using the @element
decorator (calling it as a plain function for non-decorator usage). This will
map attributes to JS properties and make the JS properties reactive.
static observedAttributeHandlers is an object where each key is a property
name to be associated with an attribute, and each value is an object with the
following shape:
/**
* Defines how values are mapped from an attribute to a JS property on a custom
* element class.
*/
export type AttributeHandler<T = any> = {
// TODO The `to` handler currently does nothing. In the future, if there is demand
// for it, this will be for property-to-attribute reflection.
to?: (propValue: T) => string | null
/**
* Define how to deserialize an attribute string value on its way to the
* respective JS property.
*
* If not defined, the attribute string value is passed to the JS property
* untouched.
*
* **Default when omitted:** `value => value`
*/
from?: (AttributeValue: string) => T
/**
* A side effect to run when the value is set on the JS property. It also
* runs on with the initial value. Avoid this if you can, and instead use
* effects. One use case of this is to call addEventListener with event
* listener values, just like with native `.on*` properties.
*
* **Default when omitted:** `() => {}` (no sideeffect)
*/
sideEffect?: (instance: Element, prop: string, propValue: T) => void
/**
* @deprecated - Define a field with the initial value instead of providing
* the initial value here. When decorators land in browsers, this will be
* removed.
*
* The default value that the respective JS property should have when the
* attribute is removed.
*
* If this is not specified, and the respective class field is defined, it
* will default to the initial value of the class field. If this is
* specified, it will take precedence over the respective field's initial
* value. This should generally be avoided, and the class field initial
* value should be relied on as the source of the default value.
*
* When defined, an attribute's respective JS property will be set to this
* value when the attribute is removed. If not defined, then the JS property
* will always receive the initial value of the respective JS class field or
* `undefined` if the field was not defined (that's the "initial value" of
* the field), when the attribute is removed.
*
* **Default when omitted:** the value of the respective class field, or
* `undefined` if the field was not defined.
*/
default?: T
/**
* Whether to convert the property name to dash-case for the attribute name.
* This option is ignore if the `name` option is set.
*
* The default is `true`, where the attribute name will be the same as the
* property name but dash-cased (and all lower case). For example, `fooBar`
* becomes `foo-bar` and `foo-bar` stays `foo-bar`.
*
* If this is set to `false`, the attribute name will be the same as the
* property name, but all lowercased (attributes are case insensitive). For
* example `fooBar` becomes `foobar` and `foo-bar` stays `foo-bar`.
*
* Note! Using this option to make a non-standard prop-attribute mapping
* will result in template type definitions (f.e. in JSX) missing the
* customized attribute names and will require custom type definition
* management.
*
* **Default when omitted:** `true`
*/
dashcase?: boolean
/**
* The name of the attribute to use. Use of this options bad practice to be
* avoided, but it may be useful in rare cases.
*
* If this is not specified, see `dashcase` for how the attribute name is
* derived from the property name.
*
* Note! Using this option to make a non-standard prop-attribute mapping
* will result in template type definitions (f.e. in JSX) missing the
* customized attribute names and will require custom type definition
* management.
*
* **Default when omitted:** the attribute name derived from the property
* name, converted to dash-case based on the `dashcase` option.
*/
name?: string
/**
* Whether to suppress warnings about the attribute attribute name clashes
* when not using default `dashcase` and `name` settings. This is
* discouraged, and should only be used when you know what you're doing,
* such as overriding a property that has `dashcase` set to `false` or
* `name` set to the same name as the attribue of another property.
*
* **Default when omitted:** `false`
*/
noWarn?: boolean
}
Here's an example of an element definition with no decorators, with HTML attributes mapped to same-name JS properties:
import {Element, element} from '@lume/element'
element(
class CoolElement extends Element {
static elementName = 'cool-element'
static observedAttributeHandlers = {
foo: {from: Number},
bar: {from: Boolean},
}
// Due to the `observedAttributeHandlers` definition, any time the `"foo"` attribute
// on the element changes, the attribute string value will be converted into a
// `Number` and assigned to the JS `.foo` property.
// Not only does `.foo` have an initial value of `123`, but when the element's
// `"foo"` attribute is removed, `.foo` will be set back to the initial value
// of `123`.
foo = 123
// Due to the `observedAttributeHandlers` definition, any time the `"bar"` attribute
// on the element changes, the attribute string value will be converted into a
// `Boolean` and assigned to the JS `.bar` property.
// Not only does `.bar` have an initial value of `123`, but when the element's
// `"bar"` attribute is removed, `.bar` will be set back to the initial value
// of `false`.
bar = false
// ...
},
)
@lume/element comes with a set of basic handlers available out of the box, each of
which are alternatives to a respective set of included decorators:
import {Element, element, attribute} from '@lume/element'
element(
class CoolElement extends Element {
static elementName = 'cool-element'
static observedAttributeHandlers = {
lorem: {}, // Effectively the same as attribute.string
foo: attribute.string, // Effectively the same as the @stringAttribute decorator. Values get passed to the JS property as strings.
bar: attribute.number, // Effectively the same as the @numberAttribute decorator. Values get passed to the JS property as numbers.
baz: attribute.boolean, // Effectively the same as the @booleanAttribute decorator. Values get passed to the JS property as booleans.
// Here we define an attribute with custom handling of the string value, in this case making it accept a JSON string that maps it to a parsed object on the JS property.
bespoke: {from: value => JSON.parse(value)}, // f.e. besoke='{"b": true}' results in the JS property having the value `{b: true}`
}
// The initial values of the JS properties define the values that the JS properties get reset back to when the corresponding attributes are removed.
lorem = 'hello'
foo = 'world'
bar = 123
baz = false
bespoke = {n: 123}
// ...
},
)
If decorator support is present (either with a build, or natively in near-future JS engines), defining attributes with decorators is simpler and more concise:
import {Element, element, numberAttribute, booleanAttribute} from '@lume/element'
@element
class CoolElement extends Element {
static elementName = 'cool-element'
// Due to the `@numberAttribute` decorator, any time the `"foo"` attribute
// on the element changes, the attribute string value will be converted into a
// `Number` and assigned to the JS `.foo` property.
// Not only does `.foo` have an initial value of `123`, but when the element's
// `"foo"` attribute is removed, `.foo` will be set back to the initial value
// of `123`.
@numberAttribute foo = 123
// Due to the `@booleanAttribute` decorator, any time the `"bar"` attribute
// on the element changes, the attribute string value will be converted into a
// `Boolean` and assigned to the JS `.bar` property.
// Not only does `.bar` have an initial value of `true`, but when the element's
// `"bar"` attribute is removed, `.bar` will be set back to the initial value
// of `true`.
@booleanAttribute bar = true
// ...
}
[!Note] Not only do decorators make the definition more concise, but they avoid surface area for human error: the non-decorator form requires defining the same-name property in both the
static observedAttributeHandlersobject and in the class fields, and if we miss one or the other then things might not work as expected.
Each of the available decorators are detailed further below.
Decorators, and the static observedAttributeHandlers object format, both work with
getter/setter properties as well:
import {Element, element, numberAttribute, booleanAttribute} from '@lume/element'
@element // The 'cool-element' name is implied from the constructor name (dash-cased)
class CoolElement extends Element {
#foo = 123
// Like with class fields, the initial value is 123, so when the "foo"
// attribute is removed the setter will receive 123.
@numberAttribute
get foo() {
return this.#foo
}
set foo(v) {
this.#foo = v
}
// ...
}
They also work with "auto accessors", which creates a prototype getter/setter:
@element
class CoolElement extends Element {
// The same rules with initial values and attribute removal apply.
@numberAttribute accessor foo = 123
@booleanAttribute accessor bar = false
// ...
}
It may be redundant to write accessor repeatedly for each property when the
alternative non-accessor format works too. The accessor format can be a
fallback in very rare cases where a performance boost is needed (for example
thousands of objects with many non-accessor properties being instantiated all at
once). Most likely there will be other performance issues at the point in
which we have thousands of elements being instantiated at once causing an any
issues.
static observedAttributeHandlersThis is an alternative for the @eventAttribute decorator (recommended, see the
@eventAttribute docs below), and will be removed after
native support for decorators lands in JS engines.
import {Element, element, attribute} from '@lume/element'
const SomeEl = element('some-el')(
class extends Element {
static observedAttributeHandlers = {
onjump: attribute.event,
}
// Also define the property explicitly (here with an optional type definition).
/** @type {EventListener | null} */
onjump = null
connectedCallback() {
super.connectedCallback()
// This element dispatches a "jump" event every second:
setInterval(() => this.dispatchEvent(new Event('jump')), 1000)
}
},
)
const el = new SomeEl()
el.onjump = () => console.log('jump!')
// or, as with "onclick" and other built-in attributes:
el.setAttribute('onjump', "console.log('jump!')")
document.body.append(el)
// "jump!" will be logged every second.
Note that for TypeScript JSX types (TSX), we want to also define event
properties on the class, for example onjump in the last example. Any
properties that start with on will be mapped to on-prefixed JSX props for
type checking. See the TypeScript section for more info.
static elementNameThe default tag name of the elements this class instantiates. When using the
@element decorator, this name value will be used if a name value is not
supplied to the decorator.
@element
class SomeEl extends LumeElement {
static elementName = 'some-el'
}
console.log(document.createElement('some-el') instanceof SomeEl) // true
static autoDefineSet this to false to tell the @element decorator (or element() when called
as a function) to not automatically define the element in the global
customElements registry. When un-specified, it defaults to true.
@element
class SomeEl extends LumeElement {
static elementName = 'some-el'
static autoDefine = false
}
const el = document.createElement('some-el')
console.log(el instanceof SomeEl) // false
customElements.define(SomeEl.elementName, SomeEl)
console.log(el instanceof SomeEl) // true
Preventing automatic definition can be useful for use with non-global CustomElementRegistry instances for scoping element definitions to ShadowRoots,
// Use a non-global element registry instead of the default global element registry:
const myRegistry = new CustomElementRegistry()
SomeEl.defineElement(myRegistry)
// Use the non-global registry for scoped element definitions inside a custom element's ShadowRoot:
class SomeElementWithScopedRegistry extends HTMLElement {
constructor() {
super()
const root = this.attachShadow({mode: 'open', customElementRegistry: myRegistry})
root.innerHTML = `<some-el></some-el>`
}
}
or for re-naming elements in case of a name collision:
SomeEl.defineElement('some-el-renamed')
static defineElementDefine this class for the given element name, or using its default name
(TheClass.elementName) if no was name given and the element was not already
defined using the @element decorator. Defaults to using the global
customElements registry unless another registry is provided (for example a
ShadowRoot-scoped registry) as a second argument.
// Defines <some-el> with the decorated class, using the passed-in name.
@element('some-el')
class SomeEl extends LumeElement {}
// Defines <other-el> with an empty subclass of SomeEl using the name passed
// into .defineElement().
const OtherEl = SomeEl.defineElement('other-el')
console.log(OtherEl === SomeEl) // false
@element
class AnotherEl extends LumeElement {
static autoDefine = false
}
// The first call to .defineElement() will not make a subclass if the class has
// not been used in a definition yet.
const El = AnotherEl.defineElement('another-el') // defines <another-el>
console.log(El === AnotherEl) // true
// The second call to .defineElement() will make a new subclass.
const El2 = AnotherEl.defineElement('yet-another-el') // defines <yet-another-el>
console.log(El2 === AnotherEl) // false
// Use a non-global element registry instead of the default global element registry:
const myRegistry = new CustomElementRegistry()
AnotherEl.defineElement('one-more-el', myRegistry)
// Use the non-global registry for scoped element definitions inside a custom element's ShadowRoot:
class SomeElementWithScopedRegistry extends HTMLElement {
constructor() {
super()
const root = this.attachShadow({mode: 'open', customElementRegistry: myRegistry})
root.innerHTML = `<one-more-el></one-more-el>`
}
}
If the class is already registered with another name, then the class will be extended with an empty subclass so that a new class is used for the new name, because a CustomElementRegistry does not allow the same class reference to be used more than once regardless of the name.
Returns the defined element class, which may be a different subclass of the class this is called on if the class this is called on is already associated with another name, otherwise returns the same class this is called on.
hasShadowWhen true, the custom element will have a ShadowRoot. Set to false
to not use a ShadowRoot. When false, styles will not be scoped via
the built-in ShadowRoot scoping mechanism, but by a much more simple
shared style sheet placed at the nearest root node, with :host
selectors converted to tag names.
@element('some-el')
class SomeEl extends Element {
hasShadow = false
template = () => html`<div>hello</div>`
}
The template content will be appended to the SomeEl instance directly, with no ShadowRoot:
<some-el id="el"></some-el>
<script>
const el = document.getElementById('el')
console.log(el.shadowRoot) // null
console.log(el.children[0]) // <div>hello</div>
</script>
[!Note] Note that without a ShadowRoot,
<slot>no longer works because it must be inside a ShadowRoot, therefore going without a ShadowRoot is useful moreso for elements that are leafs at the end of DOM tree branches and elements that will not accept any slotted children and will only havetemplatecontent as their children.
templateRootSubclasses can override the templateRoot property to provide an alternate Node for
template content to be placed into (f.e. a subclass can set it to this to have
template content appended to itself regardless of the value of hasShadow).
A primary use case for this is customizing the ShadowRoot:
@element('some-el')
class SomeEl extends Element {
// Create the element's ShadowRoot with custom options for example:
templateRoot = this.attachShadow({
mode: 'closed',
})
template = () => html`<div>hello</div>`
}
shadowOptionsDefine a shadowOptions property to specify any options for the element's
ShadowRoot. These options are passed to attachShadow(). This is a simpler
alternative to overriding templateRoot in the previous example.
@element('some-el')
class SomeEl extends Element {
shadowOptions = {mode: 'closed'}
template = () => html`<div>hello</div>`
}
styleRootSimilar to the previous templateRoot, this defines which Node to append style
sheets to when hasShadow is true. This is ignored if hasShadow is
false. It defaults to this.templateRoot, which in turn defaults to the element's
ShadowRoot.
When hasShadow is true, an alternate styleRoot is sometimes desired so
that styles will be appended elsewhere than the templateRoot. To customize
this, override it:
@element('some-el')
class SomeEl extends Element {
styleRoot = document.createElement('div')
template = () => html`
<div>
<div>${this.styleRoot}</div>
<span>hello</span>
</div>
`
}
This can be useful for fixing issues where the default append location of an
element's style sheet into the ShadowRoot conflicts with how DOM is created in
template (f.e. if the user's DOM creation in template clears the
ShadowRoot content, or etc, then the user may want to place the stylesheet
somewhere else).
createEffectThe createEffect method is a wrapper around Solid's createEffect with some differences for convenience:
createRoot is not required in order to dispose of effects created with this.createEffect()this.createEffect() will automatically be cleaned up when the element is disconnected.this.createEffect() is useful as an alternative to disconnectedCallback when
paired with Solid's onCleanup.import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'
const [count, setCount] = createSignal(0)
setInterval(() => setCount(n => ++n), 1000)
class CoolElement extends Element {
connectedCallback() {
super.connectedCallback()
// Log `count()` any time it changes.
this.createEffect(() => console.log(count()))
this.createEffect(() => {
const interval1 = setInterval(() => console.log('interval 1'), 1000)
onCleanup(() => clearInterval(interval1))
const interval2 = setInterval(() => console.log('interval 2'), 1000)
onCleanup(() => clearInterval(interval2))
})
}
}
customElements.define('cool-element', CoolElement)
// After removing the element, onCleanup fires and cleans up the intervals created in connectedCallback (not the count interval outside the element)
setTimeout(() => {
const el = document.querySelector('cool-element')
el.remove()
}, 2000)
Compare that to using disconnectedCallback:
import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'
const [count, setCount] = createSignal(0)
setInterval(() => setCount(n => ++n), 1000)
class CoolElement extends Element {
#interval1 = 0
#interval2 = 0
connectedCallback() {
super.connectedCallback()
// Log `count()` any time it changes.
this.createEffect(() => console.log(count()))
this.#interval1 = setInterval(() => console.log('interval 1'), 1000)
this.#interval2 = setInterval(() => console.log('interval 2'), 1000)
}
disconnectedCallback() {
super.disconnectedCallback()
clearInterval(this.#interval1)
clearInterval(this.#interval2)
}
}
customElements.define('cool-element', CoolElement)
:bulb:Tip:
Prefer
onCleanupinstead ofdisconnectedCallbackbecause composition of logic will be easier while also keeping it co-located and easier to read. That example is simple, but when logic grows, having to clean things up indisconnectedCallbackcan get more complicated, especially when each piece of creation logic and cleanup logic is multiple lines long and interleaving them would be harder to read. Plus, putting them in effects makes them creatable+cleanable if signals in the effects change, not just if the element is connected or disconnected. For example, the following element cleans up the interval any time the signal changes, not only on disconnect:
import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'
const [count, setCount] = createSignal(0)
setInterval(() => setCount(n => ++n), 1000)
class CoolElement extends Element {
connectedCallback() {
super.connectedCallback()
// Log `count()` any time it changes.
this.createEffect(() => console.log(count()))
this.createEffect(() => {
// Run the interval only during moments that count() is an even number.
// Whenever count() is odd, the running interval will be cleaned up and a new interval will not be created.
// Also, when the element is disconnected (while count() is even), the interval will be cleaned up.
if (count() % 2 !== 0) return
const interval = setInterval(() => console.log('interval'), 100)
onCleanup(() => clearInterval(interval))
})
}
}
customElements.define('cool-element', CoolElement)
// After removing the element, onCleanup fires and cleans up any interval currently created in connectedCallback (not the count interval outside the element)
setTimeout(() => {
const el = document.querySelector('cool-element')
el.remove()
}, 2500)
The beauty of this is we can write logic based on signals, without worrying
about disconnectedCallback, and we'll rest assured things clean up properly.
Cleanup logic is co-located with the pieces they are relevant to, which opens
the door to powerful compositional patterns...
Using decorators (if available in your build, or natively in your JS engine)
instead of static observedAttributeHandlers or static events is more concise
and less error prone.
Here's the list of included attribute decorators and the attribute handler equivalents:
@stringAttribute foo in place of foo: {}@stringAttribute foo in place of foo: attribute.string@numberAttribute foo in place of foo: attribute.number@booleanAttribute foo in place of foo: attribute.boolean@eventAttribute foo in place of foo: attribute.event@jsonAttribute foo in place of foo: attribute.json[!Warning] When using attribute decorators, the
@elementdecorator is also required on the class, or the attribute decorators won't work.
Below are more details on each decorator:
@elementThe star of the show, a decorator for defining a custom element.
When passed a name string, it will be the element's tag name:
import {Element, element} from '@lume/element'
@element('my-element') // <my-element> will be defined
class CoolElement extends Element {
// ...
}
[!Note] Make sure you extend from the
Elementbase class from@lume/elementwhen using the@elementdecorator.
When not passed a name string, the name is derived from the dash-cased name of the class:
import {Element, element} from '@lume/element'
@element // The 'cool-element' name is implied
class CoolElement extends Element {
// ...
}
A second boolean argument can disable automatic definition in the global
customElements registry. The constructor's .defineElement() method can then
be used to manually trigger the definition using the given name:
import {Element, element} from '@lume/element'
const autoDefine = false
@element('cool-element', autoDefine)
class CoolElement extends Element {
// ...
}
CoolElement.defineElement() // uses the global customElements to define <cool-element>
// or
const myRegistry = new CustomElementRegistry()
CoolElement.defineElement(myRegistry) // uses a non-global registry to define <cool-element>
// Use a non-global registry for scoped element definitions inside a custom element's ShadowRoot:
class SomeElementWithScopedRegistry extends HTMLElement {
constructor() {
super()
const root = this.attachShadow({mode: 'open', customElementRegistry: myRegistry})
root.innerHTML = `<cool-element></cool-element>`
}
}
A custom name can be passed to .defineElement() too:
CoolElement.defineElement('other-element') // defines <other-element> (even if `<cool-element>` is already defined)
@element also accepts options as an object:
const autoDefine = false
@element({elementName: 'cool-element', autoDefine})
class CoolElement extends Element {
// ...
}
const autoDefine = false
@element({autoDefine}) // The "cool-element" name is implied.
class CoolElement extends Element {
// ...
}
Without passing arguments to @element, options can be specified using
static class fields:
const autoDefine = false
@element
class CoolElement extends Element {
static elementName = 'cool-element'
static autoDefine = autoDefine
// ...
}
The last format is nice and clean if you like all the aspects of your class defined within the class, or your minifier is mangling your class name. It is also useful in TypeScript to avoid repeating the class name multiple times:
const autoDefine = false
@element
class CoolElement extends Element {
static readonly elementName = 'cool-element'
static readonly autoDefine = autoDefine
// ...
}
declare global {
interface HTMLElementTagNameMap {
// This avoids error-prone repitition of 'cool-element' in multiple locations.
[CoolElement.elementName]: CoolElement
}
}
See more on TypeScript below.
@attributeA decorator for defining a generic element attribute. The name of the property is mapped from camelCase to dash-case.
The @attribute decorator is effectively the same as the @stringAttribute decorator.
import {Element, element, attribute} from '@lume/element'
@element
class CoolElement extends Element {
@attribute firstName = null // the attribute name is first-name
// ...
}
When an attribute is removed, the JS property will receive the default value determined by the initial value of the JS property, ensuring consistency: when all attributes of an element are removed, the values the JS properties will have is known based on the class definition.
Sample usage of the attribute from the outside:
const el = document.querySelector('cool-element')
el.setAttribute('first-name', 'Superman')
console.log(el.firstName) // logs "Superman"
el.removeAttribute('first-name')
console.log(el.firstName) // logs null
Had we defined a different initial value,
@attribute firstName = 'Batman'
then removing the attribute would have set the JS property back to that non-null value:
const el = document.querySelector('cool-element')
el.setAttribute('first-name', 'Superman')
console.log(el.firstName) // logs "Superman"
el.removeAttribute('first-name')
console.log(el.firstName) // logs "Batman"
The outcome is predictable and consistent.
For TypeScript, if the initial value is a string and we're using @attribute (or
@stringAttribute), then no type annotation is needed because it will always
receive a string (f.e. even when the attribute is removed) and the type will be
inferred from the initial value:
@element
class CoolElement extends Element {
@attribute firstName = 'Batman' // always a `string`
// ...
}
You could of course make the string type more specific,
@element
class CoolElement extends Element {
@attribute firstName: 'Batman' | 'Robin' = 'Batman'
// ...
}
but note that this does not prevent any string value being set via the attribute.
You can of course make a broader type that accepts a string from the element
attribute, but also other types via the JS property directly, but you'd
generally want to avoid this, unless you're using a getter/setter to coerce
setter values into a single consistent type that the getter always returns (like
how the builtin el.style= can accept a string but the return value of
el.style is always an object), or the user's input is always unchanged and
mapped separately to internal structures:
import {Element, element, attribute} from '@lume/element'
@element
class CoolElement extends Element {
@attribute firstName: string | number = 'Batman'
// ...
}
const el = document.querySelector('cool-element')
el.firstName = 123 // ok
The @attribute decorator is also useful for defining custom handling of
attributes. For example, the following shows how we can define an attribute that
can accept JSON string values by providing an
AttributeHandler definition, using the from option to
define how string values from the attribute are coerced when they are assigned
to the JS property:
// Here, `attribute` is not called as a decorator. When `attribute` is given an
// argument that defines how to handle an attribute, it will return a new
// decorator function.
const jsonAttribute = attribute({from: str => JSON.parse(str)})
Now we can use the new jsonAttribute decorator in an element class:
@element
class CoolElement extends Element {
@jsonAttribute someValue = {foo: 123}
// ...
}
Now in HTML/DOM the attribute can accept JSON strings:
<cool-element id="el" some-value='{"foo": 456}'></cool-element>
<script>
console.log(el.someValue) // logs the object {foo: 456}
el.setAttribute('foo', '{"foo": 789}')
console.log(el.someValue) // logs the object {foo: 789}
</script>
Note that we could have used attribute() as a decorator directly,
@element
class CoolElement extends Element {
@attribute({from: str => JSON.parse(str)}) someValue = {foo: 123}
// ...
}
but then the result would not have been saved into a re-usable jsonAttribute
variable, and the class field definition would have been a little messier to
read.
What new attribute decorators will you make?
@stringEnumAttribute that accepts only certain string values otherwise
throws an error?@cssColorAttribute that accepts only CSS-format color strings otherwise
throws an error?@threeColorAttribute that coerces CSS color values into Three.js Color
objects?The sky is not the limit!
@stringAttributeThe @stringAttribute decorator is effectively the same as the @attribute
decorator, but without the ability to accept arguments to define new attribute
decorators. See the previous section.
This is preferable over plain @attribute for keeping the class definition
semantic and clear. Prefer using @attribute for custom attribute types that
are not supported out of the box.
@numberAttributeA decorator that defines an attribute that accepts a number. Any value the
attribute receives will be passed to the JS property, which is then coerced into
a number with parseFloat. The JS property will convert a null value
(attribute removed) to the default value defined by the initial property value,
and will convert any string into a number (if the string is invalid the property
value will result in NaN).
import {Element, element, numberAttribute} from '@lume/element'
@element
class CoolElement extends Element {
@numberAttribute age = 10
// ...
}
const el = document.querySelector('cool-element')
el.setAttribute('age', '20')
console.log(el.age) // logs 20
console.log(typeof el.age) // logs "number"
el.removeAttribute('age')
console.log(el.age) // logs 10
console.log(typeof el.age) // logs "number"
el.age = '30' // assign a string (type error in TypeScript)
console.log(el.age) // logs 30
console.log(typeof el.age) // logs "number"
For TypeScript, you don't need a type annotation if the initial value is a
number. Add a type annotation only if you use a non-number initial value, f.e.
number | SomeOtherType, but that is not recommended:
import {Element, element, numberAttribute} from '@lume/element'
@element
class CoolElement extends Element {
@numberAttribute age: 'ten' | number = 'ten'
// ...
}
const el = document.querySelector('cool-element')
el.setAttribute('age', '20')
console.log(el.age) // logs 20
console.log(typeof el.age) // logs "number"
el.removeAttribute('age')
console.log(el.age) // logs "ten"
console.log(typeof el.age) // logs "string"
el.age = 'ten'
console.log(el.age) // logs "NaN", which is confusing (hence, avoid doing this).
console.log(typeof el.age) // logs "number"
@booleanAttributeA decorator that defines a boolean attribute. Any value the attribute receives
will be passed to the JS property, which is then coerced into a boolean. The
JS property will convert a null value (attribute removed) to the default value
defined by the initial property value, and will convert any string into boolean.
All string values except "false" result in the boolean true, and the string
"false" results in the boolean false.
To mimick the same behavior as boolean attributes on built-in elements where the
presence of the attribute is true, and absence of the attribute is false, start
with an initial value of false:
import {Element, element, booleanAttribute} from '@lume/element'
@element
class CoolElement extends Element {
@booleanAttribute hasPizza = false
// ...
}
If the attribute value exists, the JS property will receive true, except if
the value of the attribute is explicitly "false":
const el = document.querySelector('cool-element')
el.setAttribute('has-pizza', '')
console.log(el.age) // logs true
console.log(typeof el.age) // logs "boolean"
el.setAttribute('has-pizza', 'blah blah')
console.log(el.age) // logs true
console.log(typeof el.age) // logs "boolean"
el.removeAttribute('has-pizza')
console.log(el.age) // logs false
console.log(typeof el.age) // logs "boolean"
// A literal "false" value is special and is treated as false.
el.setAttribute('has-pizza', 'false')
console.log(el.age) // logs false
console.log(typeof el.age) // logs "boolean"
Here is the equivalent example in HTML describing the values of has-pizza:
<!-- hasPizza == true -->
<cool-element has-pizza></cool-element>
<!-- hasPizza == true -->
<cool-element has-pizza="true"></cool-element>
<!-- hasPizza == true -->
<cool-element has-pizza="blah blah"></cool-element>
<!-- hasPizza == false -->
<cool-element></cool-element>
<!-- hasPizza == false -->
<cool-element has-pizza="false"></cool-element>
The purpose of treating "false" as explicitly false is that this makes it
possible to have the attribute be present while still being able to express both
values,
<cool-element has-pizza="true"></cool-element> <cool-element has-pizza="false"></cool-element>
while also having the option to express the same thing using only attribute presence:
<cool-element has-pizza></cool-element> <cool-element></cool-element>
If you start with an initial value of true, then when the attribute is removed
or never existed, the JS property will be true, which again is useful for
predictability of default state.
import {Element, element, booleanAttribute} from '@lume/element'
@element
class CoolElement extends Element {
@booleanAttribute hasPizza = true
// ...
}
In this case, only an attribute value of "false" can set the JS property to false:
const el = document.querySelector('cool-element')
el.setAttribute('has-pizza', '')
console.log(el.age) // logs true
console.log(typeof el.age) // logs "boolean"
el.setAttribute('has-pizza', 'blah blah')
console.log(el.age) // logs true
console.log(typeof el.age) // logs "boolean"
el.removeAttribute('has-pizza')
console.log(el.age) // logs true
console.log(typeof el.age) // logs "boolean"
// Only a literal value of "false" will cause the JS property to be false in this case.
el.setAttribute('has-pizza', 'false')
console.log(el.age) // logs false
console.log(typeof el.age) // logs "boolean"
Equivalent HTML:
<!-- hasPizza == true -->
<cool-element has-pizza></cool-element>
<!-- hasPizza == true -->
<cool-element has-pizza="foo"></cool-element>
<!-- hasPizza == true -->
<cool-element has-pizza="blah blah"></cool-element>
<!-- hasPizza == true -->
<cool-element></cool-element>
<!-- hasPizza == false -->
<cool-element has-pizza="false"></cool-element>
In this form, with the property initial value as true, then the following two
are identical (the JS property is true in either case),
<cool-element has-pizza></cool-element> <cool-element></cool-element>
and expressing both true and false side by side would require explicit values:
<cool-element has-pizza="true"></cool-element> <cool-element has-pizza="false"></cool-element>
:bulb:Tip:
Avoid attribute values like
has-pizza="blah blah", because they are not semantic. When the default JS property value isfalse, always use the formhas-pizza="false"or no attribute forfalse, andhas-pizzaorhas-pizza="true"fortrue. When the default JS property value istrue, always use the formhas-pizza="false"forfalse, andhas-pizza,has-pizza="true", or no attribute, fortrue.
@eventAttributeUse this decorator to create event listener attributes/properties, the same as with built-in event attributes/properties such as "onclick".
import {Element, element, eventAttribute} from '@lume/element'
@element('some-el')
class MyEl extends Element {
/** @type {EventListener | null} */
@eventAttribute onjump = null
connectedCallback() {
super.connectedCallback()
// This element dispatches a "jump" event every second:
setInterval(() => this.dispatchEvent(new Event('jump')), 1000)
}
}
const el = new SomeEl()
el.onjump = () => console.log('jump!')
// or, as with "onclick" and other built-in attributes:
el.setAttribute('onjump', "console.log('jump!')")
document.body.append(el)
// "jump!" will be logged every second.
Note that besides the event properties working in JS, the attributes also work
in plain HTML as with native event attributes such as onclick:
<body>
<my-el onjump="console.log('jump!')"></my-el>
</body>
@jsonAttributeA decorator that defines an attribute that accepts JSON strings. In general, you want to avoid such complex attributes and instead provide a set of attributes that accept simple values. Setting (or deserializing) whole objects at a time for state changes can be too costly in performance sensitive situations.
This can be usedul in certain scenarios such as wrapping a JavaScript API that accepts an object with unknown properties; in such a scenario we wouldn't know which attribute to define on the element, so we simply pass the object along:
@element
class HTMLInterfaceForSomeAPI extends Element {
static elementName = 'some-api'
@jsonAttribute data = {}
connectedCallback() {
super.connectedCallback()
this.createEffect(() => {
const obj = new SomeAPI(data)
// ...
onCleanup(() => obj.dispose())
})
}
}
<some-api data='{"someValue": 123}'></some-api> <some-api data='{"otherValue": 456}'></some-api>
@signalThis is from classy-solid for creating
signal properties, but because @element is composed with classy-solid's
@reactive class decorator, a non-attribute signal property can be defined
without also having to use classy-solid's @reactive decorator on the class:
import {Element, element, booleanAttribute} from '@lume/element'
import {reactive, signal} from 'classy-solid'
// Non element class, requires `@reactive` for fields decorated with `@signal`:
@reactive
class Something {
@signal foo = 123 // This will be reactive
}
// An element class decoratorated with `@element` (or passed to `element()` when
// not using decorators) does not also need to be decorated with `@reactive`:
@element
class CoolElement extends Element {
// hasPizza will be reactive but an attribute will not be observed for this
// property, and the property can only be set via JS.
@signal hasPizza = false
// This property *does* get updated when a `has-drink` attribute is updated, and is also reactive.
@booleanAttribute hasDrink = false
// ...
}
@noSignalOnce in a blue moon you might need to define an attribute property that is not
reactive, for some reason. Avoid it if you can, but you can do it with
@noSignal:
import {Element, element, booleanAttribute, noSignal} from '@lume/element'
@element
class CoolElement extends Element {
// This property gets updated when a `has-drink` attribute is updated, but it is not reactive.
@booleanAttribute @noSignal hasDrink = false
}
This is more useful on a getter/setter where you may implement your own reactivity for the property:
import {Element, element, booleanAttribute, noSignal} from '@lume/element'
@element
class CoolElement extends Element {
#hasDrink = false
// This property gets updated when a `has-drink` attribute is updated, and
// it is not reactive due to the `@booleanAttribute` decorator but due to a
// custom implementation in the getter/setter (for example, maybe the
// getter/setter reads from and writes to a Solid signal.
@booleanAttribute @noSignal get hasDrink() {
// ...
return this.#hasDrink
}
@booleanAttribute @noSignal set hasDrink(value) {
// ...
this.#hasDrink = value
}
}
[!Note] Make sure the
@noSignaldecorator is listed after the attribute decorator. This will not work:
class CoolElement extends Element {
// This won't work because the attribute decorator will run before the
// noSignal decorator so the attribute decorator will miss the signal that
// it should skip the signal (pun intended!).
@noSignal @booleanAttribute hasDrink = false
}
The from handler of a newly-defined attribute decorator (defining new
attribute decorators is described in the @attribute doc above) can throw an
error when an invalid string is encountered. Expanding the previous jsonAttribute example:
const jsonAttribute = attribute({
from(str){
const result = JSON.parse(str)
if (/* some condition not met with result */) throw new Error('...describe the error...')
return result
}
})
This error handling will work regardless if setting an attribute, or setting a string via the JS property.
An alternative approach is to throw an error in the setter of an
@attribute-decorated property, which can be useful for existing code that
might already exist where the @attribute decorator is being added:
@element
class CoolElement extends Element {
#foo = 123
@attribute get someValue() {
return this.#foo
}
@attribute set someValue(value) {
if (/* some condition not met with value */) throw new Error('...error description...')
this.#foo = value
}
}
Here are the recommended types for properties depending on the type of attribute being defined, with non-null initial values:
import {Element, element, attribute, stringAttribute, numberAttribute, booleanAttribute} from '@lume/element'
@element
class CoolElement extends Element {
static readonly elementName = 'cool-element'
@attribute firstName: string = 'John'
@stringAttribute lastName: string = 'Doe'
@numberAttribute age: number = 75
@booleanAttribute likesPizza: boolean = true
// jsonAttribute is implemented as an example above
@jsonAttribute info: SomeObject = {
/*...*/
}
// ...
}
If properties are initialized with null values, add | null to each type:
@element
class CoolElement extends Element {
static readonly elementName = 'cool-element'
@attribute firstName: string | null = null
@stringAttribute lastName: string | null = null
@numberAttribute age: number | null = null
@booleanAttribute likesPizza: boolean | null = null
// jsonAttribute is implemented as an example above
@jsonAttribute info: SomeObject | null = null
// ...
}
All attribute properties can technically accept strings too, as this is how attribute string values get coerced in case of non-string attributes. Although it is not recommended, this aspect of the properties can be exposed if needed:
@element
class CoolElement extends Element {
static readonly elementName = 'cool-element'
@attribute firstName: string = 'John'
@stringAttribute lastName: string = 'Doe'
@numberAttribute age: `${number}` | number = 75
@booleanAttribute likesPizza: `${boolean}` | boolean = true
// ...
}
const el = new CoolElement()
el.age = '80' // no type error here
console.log(el.age, typeof el.age) // logs "80 number"
el.age = 'blah' // type error, 'blah' is not assignable to a string with number format defined by `${number}`.
It is nice to not include the string types, especially because the string
values are always coerced by the attribute from handler, and JS/TS users can
set the actual values directly (f.e. numbers or booleans). You will always
receive a number when reading a JS property decorated with
@numberAttribute, for example, so including the string type could make things
confusing and less ideal. For example, when reading the value of a
@numberAttribute property, the following may be redundant and annoying when
reading the value, especially in TypeScript:
if (typeof el.age === 'number') { // this check is unnecessary/annoying, required for types to check out
const n: number = el.age
}
// or
const n: number = el.age as number // unnecessary/annoying cast in this case
if (typeof el.age === 'string') console.log('this will never be logged')
(Note this section is only for Solid.js, as other frameworks like React or Preact do not have DOM-returning JSX expressions.)
Load the required JSX types in one of two ways:
Import the types locally within particular files where JSX is used (this is useful for preventing type conflicts if you have other files that use React JSX types or other JSX types):
/* jsxImportSource solid-js */
Place the jsxImportSource in your tsconfig.json to have it apply to all
files (this works great if you use only one form of JSX types in your
project, but if you have files with different types of JSX, you'll want to
use option 1 instead).
{
"compilerOptions": {
/* Solid.js Config */
// Note, you need to use an additional tool such as Babel, Vite, etc, to
// compile Solid JSX. `npm create solid` will scaffold things for you.
"jsx": "preserve",
"jsxImportSource": "solid-js"
}
}
In TypeScript, all JSX expressions have the type JSX.Element. But Solid's JSX
expressions return actual DOM nodes, and we want the JSX expression types to
reflect that fact. For this we have a set of convenience helpers to cast JSX
expressions to DOM element types in the @lume/element/dist/type-helpers.js
module.
Modifying the example from Easily create and manipulate DOM for TypeScript, it would look like the following.
import {createSignal} from 'solid-js'
import {div} from '@lume/element/dist/type-helpers.js'
const [count, setCount] = createSignal(0)
setInterval(() => setCount(count() + 1), 1000)
const el = div(
<div>
<h1 data-count={count()}>The count is: {count()}</h1>
</div>,
)
el.setAttribute('foo', 'bar')
document.body.appendChild(el)
The main differences from plain JS are
@jsxImportSource comment to place JSX types into scope. This is
required, or TypeScript will not know what the types of elements in JSX
markup are. Alternative to comments, configure it in tsconfig.json's
compilerOptions.div() helper function explicitly returns the type HTMLDivElement so
that the el variable will be typed as HTMLDivElement instead of
JSX.Element. Under the hood, the div() function is an identity function
at runtime, it simply returns whatever you pass into it, and serves only as a
convenient type cast helper.[!Warning] Keep in mind to use the correct type helper depending on what the root element of the JSX expression is. For for example, if the root of a JSX expression is a
<menu>element then we need to use themenu()helper like follows.
import {createSignal} from 'solid-js'
import {menu} from '@lume/element/dist/type-helpers.js'
// ...
// The type of `el` will be `HTMLMenuElement`.
const el = menu(
<menu>
<h1 data-count={count()}>The count is: {count()}</h1>
</menu>,
)
If the wrong helper is used, then it will effectively cast the expression to
the wrong type. For example, in the next snippet the el variable will be of
type HTMLDivElement despite the fact that at runtime we will be have an
HTMLMenuElement instance.
import {div, button} from '@lume/element/dist/type-helpers.js'
// GOOD.
const el = button(<button>...</button>)
// BAD! Don't do this! Remember to double check, because the helpers are not
// type safe, you will not get an error here, and el2 will incorrectly be type
// HTMLDivElement.
const el2 = div(<menu>...</menu>)
Without the type helpers, we would need to write more verbose code like the following to have the proper types, but note that the following is also not type safe:
// GOOD.
const el = (<menu>...</menu>) as any as HTMLMenuElement
// BAD! Don't do this! Remember to double check, because the helpers are not
// type safe, you will not get an error here.
const el2 = (<menu>...</menu>) as any as HTMLDivElement
(For type definitions for function components, see Solid.js docs).
Example: 'kitchen-sink-tsx'
First set up jsxImportSource as mentioned above.
To give our Custom Elements type checking for use with DOM APIs, and type
checking in Solid JSX, we can add the element type definition to
HTMLElementTagNameMap and JSX.IntrinsicElements. Use the ElementAttributes
helper to specify which attributes/properties should be exposed in the JSX type
(we do not want to expose methods for example, or we may want to skip exposing
some properties that are implementation details such as those prefixed with
underscores to represent that they are internal, etc):
import type {ElementAttributes} from '@lume/element'
import {Element, element, stringAttribute, numberAttribute, eventAttribute} from '@lume/element'
// List the properties that should be picked from the class type for JSX props.
// Note! Make sure that the properties listed are either decorated with
// attribute decorators, or that they are on* event properties.
export type CoolElementAttributes = 'coolType' | 'coolFactor' | 'oncoolness'
@element
export class CoolElement extends Element {
static readonly elementName = 'cool-element'
@stringAttribute coolType: 'beans' | 'hair' = 'beans'
@numberAttribute coolFactor = 100
// ^ NOTE: These are the camelCase equivalents of the attributes defined above.
// For any given event our element will dispatch, define an event prop with
// the event name prefixed with 'on', and that accepts an event listener
// function or null.
@eventAttribute oncoolness: ((event: CoolnessEvent) => void) | null = null
// This property will not appear in the JSX types because it is not listed in
// the `CoolElementAttributes` that are passed to `ElementAttributes` below.
notJsxProp = 123
// ... Define the class as described above. ...
}
/** This an event that our element dispatches, for example. */
class CoolnessEvent extends Event {
constructor() {
super('coolness', {...})
}
}
// Add our element to the list of known HTML elements. This makes it possible
// for browser APIs to have the expected return types. For example, the return
// type of `document.createElement('cool-element')` will be `CoolElement`.
declare global {
interface HTMLElementTagNameMap {
[CoolElement.elementName]: CoolElement
}
}
// Hook up the type for use in Solid JSX templates
declare module 'solid-js' {
namespace JSX {
interface IntrinsicElements {
[CoolElement.elementName]: ElementAttributes<CoolElement, CoolElementAttributes>
}
}
}
Now when we use <cool-element> in Solid JSX, it will be type checked:
return (
<cool-element
// cool-type={123} // Type error: number is not assignable to 'beans' | 'hair'
// cool-factor={'foo'} // Type error: string is not assignable to number
cool-type="hair" // ok
cool-factor="200" // ok
oncoolness={() = console.log('coolness happened')} // ok
></cool-element>
)
Example: 'kitchen-sink-react19'
Defining the types of custom elements for React JSX is similar as for Solid JSX above, but with some small differences for React JSX:
// tsconfig.json
{
"compilerOptions": {
/* React Config */
"jsx": "react-jsx",
"jsxImportSource": "react" // React >=19 (Omit for React <=18)
}
}
import type {ReactElementAttributes} from '@lume/element/dist/framework-types/react.js'
// ... the same CoolElement class and HTMLElementTagNameMap definitions as above ...
// Hook up the type for use in React JSX templates
declare module 'react' {
namespace JSX {
interface IntrinsicElements {
[CoolElement.elementName]: ReactElementAttributes<CoolElement, CoolElementAttributes>
}
}
}
Now when we use <cool-element> in React JSX, it will be type checked:
return (
<cool-element
// coolType={123} // Type error: number is not assignable to 'beans' | 'hair'
// coolFactor={'foo'} // Type error: string is not assignable to number
coolType="hair" // ok
coolFactor="200" // ok
oncoolness={() = console.log('coolness happened')} // ok
></cool-element>
)
[!Note] You may want to define React JSX types for your elements in separate files than the Solid JSX types, and have React users import those separate files if they need the types, and similar if you make JSX types for Vue, Svelte, etc (we don't have helpers for those other fameworks yet, but you can manually augment JSX in that case, contributions welcome!).
Example: 'kitchen-sink-preact'
The definition is exactly the same as the previous section for React JSX. Define
the element types with the same ReactElementAttributes helper as described
above.
In our TypeScript compilerOptions we should make sure to link to the React
compatibility layer:
{
"compilerOptions": {
/* Preact Config */
"jsx": "react-jsx",
"jsxImportSource": "preact",
"paths": {
"react": ["./node_modules/preact/compat/"],
"react-dom": ["./node_modules/preact/compat/"]
}
}
}
[!Note] A default Preact app created with
npm init preactwill already have this set up.
The rest is the same as with defining types in a React app.
Example: 'kitchen-sink-angular'
Register the element type for Angular like so:
// ... the same CoolElement class definition as above ...
// Type checking in angular is currently limited to only knowing the custom
// element tag names (from HTMLElementTagNameMap), but there is no way to
// provide types of template props for type checking. For now, this is the best
// we can do. See:
// https://github.com/angular/angular/issues/58483
declare global {
interface HTMLElementTagNameMap {
[CoolElement.elementName]: CoolElement
}
}
Example: 'kitchen-sink-vue'
Register the element type for Vue like so:
import type {VueElementAttributes} from '@lume/element/dist/framework-types/vue.js'
// ... the same CoolElement class and HTMLElementTagNameMap definitions as above ...
// Hook up the type for use in Vue templates
declare module 'vue' {
interface GlobalComponents {
[CoolElement.elementName]: VueElementAttributes<CoolElement, CoolElementAttributes>
}
}
Example: 'kitchen-sink-svelte'
Register the element type for Svelte like so:
import type {SvelteElementAttributes} from '@lume/element/dist/framework-types/vue.js'
// ... the same CoolElement class and HTMLElementTagNameMap definitions as above ...
// Hook up the type for use in Svelte templates
declare module 'svelte/elements' {
interface SvelteHTMLElements {
[CoolElement.elementName]: SvelteElementAttributes<CoolElement, CoolElementAttributes>
}
}
Example: 'kitchen-sink-stencil'
Register the element type for Stencil.js like so:
import type {StencilElementAttributes} from '@lume/element/dist/framework-types/stencil.js'
// ... the same CoolElement class and HTMLElementTagNameMap definitions as above ...
// Hook up the type for use in Svelte templates
declare module '@stencil/core' {
export namespace JSX {
interface IntrinsicElements {
[CoolElement.elementName]: StencilElementAttributes<CoolElement, CoolElementAttributes>
}
}
}
Given a custom element definition like so,
@element
class MyEl extends Element {
static readonly elementName = 'my-el'
#position = new Vec3()
get position(): Vec3 {
return this.#position
}
set position(value: Vec3 | `${number} ${number} ${number}` | [number, number, number]) {
const {x, y, z} = parseValue(value)
this.#position.set(x, y, z)
}
}
using it in JSX or other framework templates will show type errors for a use cases like this one,
function MyComponent() {
return (
<>
<my-el position={[1, 2, 3]} />
<my-el position={'1 2 3'} />
</>
)
}
despite the fact that [1, 2, 3] and "1 2 3" are both valid values that the
element's position setter can accept.
We can fix this by using a __set__-prefixed property that matches the
getter/setter name to define the setter type that will appear in JSX/framework
templates:
@element
class MyEl extends Element {
static readonly elementName = 'my-el'
#position = new Vec3()
get position(): Vec3 {
return this.#position
}
set position(value: this['__set__position']) {
const {x, y, z} = parseValue(value)
this.#position.set(x, y, z)
}
// Add a note telling people not to use this property, it is for template type definition only.
/** @deprecated Do not use this directly. */
declare __set__position: Vec3 | `${number} ${number} ${number}` | [number, number, number]
}
Note that we re-used the __set__position type for the setter to avoid having
to write tye type definition twice. With this additional type-only property defined, the previous
MyComponent JSX example will not have type errors and will allow the values.
See https://solid.js.com, https://primitives.solidjs.community, and
https://github.com/lume/classy-solid for APIs that are useful with
@lume/element.
Also see Custom Element (i.e. Web Component) systems that are alternative to
@lume/element:
FAQs
Create Custom Elements with reactivity and automatic re-rendering.
The npm package @lume/element receives a total of 30 weekly downloads. As such, @lume/element popularity was classified as not popular.
We found that @lume/element demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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